Long term economic and environmental concerns with the current petroleum-based economy have driven the development of approaches that convert renewable sources to organic chemicals to replace those derived from petroleum feed stocks. Production of biofuels, such as ethanol or butanol, through microorganisms has been a research focus in recent years, and significant progress has been made in this area. At the same time, there remains a great need for development of biorefining processes that utilize microorganisms to convert renewable sources into industrially useful chemicals.
Esters, in particular, are in great demand for a variety of industrial and cosmetic applications. Isobutyl isobutyrate is a popular retarder solvent for a variety of lacquers and thinners, and it can be found in numerous painted coatings. It is also used as an insect repellant. The estimated United States annual production of isobutyl isobutyrate is approximately four thousand metric tons. Isobutyl acetate, ethyl isobutyrate, isoamyl acetate, and phenethyl acetate are also used as lacquer solvents. In addition to their industrial uses, acetate and isobutyrate esters are naturally found in plants, and they are used in various cosmetics, fragrances, and food products for their fruity and/or floral aromas. For example, isobutyl isobutyrate smells like pineapple, and isoamyl acetate has a strong, banana-like odor.
The current method of producing these esters involves individually producing the constituent alcohols and carboxylic acids, then esterifying them through chemical synthesis or enzymatic reactions. This two-step process requires individual production and purification steps to generate each constituent and further processing and purification steps to yield the final ester. Much of the production of the constituent alcohols and carboxylic acids depends heavily upon petroleum, which is increasingly expensive and associated with global health and environmental concerns.
In view of these facts and the growing global demand for acetate and isobutyrate esters, a significant need exists for esters produced from renewable sources. Specifically, recombinant bacteria are needed for cost-efficient biosynthesis of acetate and isobutyrate esters.